Device for feeding a high frequency oscillating tool

ABSTRACT

This invention relates to an arrangement for driving a high-frequency oscillating tool arrangement (1) which includes, inter alia, a device (1a) whose form changes with a change in voltage, utilizing an electric drive circuit (2) constructed to generate alternating voltage which can be connected to the device and the frequency of which is adapted, through a first control circuit (7), to a value (C1, L1) which momentarily corresponds to the resonance frequency of the reactive element which varies during a working operation. The first control circuit (7) is constructed to control momentary frequency in dependence on momentary phase difference between the current and voltage values of the alternating voltage. A second control circuit (4) is intended to control an inductive element (12) included in an oscillation circuit having a capacitive element (C2) corresponding, inter alia, to the form-changing device, such that the inductive element (C2) will obtain a value (1a) which corresponds to resonance for the prevailing alternating voltage frequency.

TECHNICAL FIELD

The present invention relates to a system for driving a tool arrangementwhich oscillates at high frequency, and then particularly to a systemfor driving a tool tip which is intended for working a workpiece andwhich oscillates at high frequency and which can exhibit a resonancepattern when driven with the aid of an alternating voltage to which aparticular frequency is assigned, a so-called resonance frequency.

Tool configurations which include readily attached and detached tooltips of the aforedescribed kind are previously known and include adevice, such as a piezoelectric crystal, which changes form whensubjected to changes in the voltage and in which the crystal isinfluenced by an electric drive circuit which is constructed to generatean alternating voltage whose frequency normally lies within the range of20-40 kHz.

Tool configurations of this kind normally include a holder or handlewhich surrounds the crystal and holds the crystal firmly clamped, and towhich there can be fitted a tool tip, such as a chisel, a file, grindingmeant and the like, by means of which a workpiece can be worked andwhich are intended to be moved reciprocatingly during the actual workingprocess.

BACKGROUND ART

Each tool arrangement of the aforesaid kind intended for driving ahigh-frequency oscillating machine tool comprising one or more crystalswhich change their form when subjected to a change in voltage and whichare incorporated in a tool holder and which utilize an electric drivecircuit constructed to produce an alternating voltage which can beapplied to the crystal, is fitted with a tool tip.

As a result of its construction, the material from which it is made, andits size and shape, each such tool tip, has a resonance frequency atwhich the energy losses are low. However, when pressure is brought tobear on the tool tip as it performs work, the resonance frequency willchange momentarily and consequently there have been proposed variouscontrol circuits or regulating circuits (first control circuits) whichstrive to cause the high frequency oscillation or the alternatingvoltage applied to the crystal to lie in a momentary resonancefrequency. In principle, the resonance frequency is determinedelectrically by two parallel-connected electrical oscillation circuits,where a first resonance circuit can be considered to constitute acapacitance and an inductance value which is dependent on the extent towhich the tool tip is loaded, and therewith varies in time, and where asecond resonance circuit can be considered to comprise a substantiallyfixed capacitance belonging to or related to the crystal and asubstantially fixed inductance incorporated in the drive circuit.

It is also known that a given change in resonance frequency will occuras a result of operating conditions and when the tool tip is loaded.This change is normally of such small magnitude that the aforesaidsecond resonance circuit, with said fixed inductance, will stillfunction very effectively provided that the tool tip is suitably adaptedto a selected resonance frequency and provided that the operatingconditions are suitably selected within narrow limits.

It has also been proposed to use a frequency controllable supply voltagewhose frequency can be adapted to momentary resonance frequencies, byusing a first control circuit.

Previously known constructions of this kind enable frequency to becontrolled or regulated within narrow limits, say +/-2 kHz, since onecontrol circuit, constructed to detect and regulate towards a fixedminimum impedence, can readily slide over resonance criteria (100 atFIG. 6B) and when detecting and regulating towards a prevailing phaseposition, between the current and voltage values, there is no positiveimpedence phase around the series resonance (200 and 200' at FIG. 6B and6C).

It has been found, however, that when such a drive circuit constructionis used at very high loads and/or at prevailing idling frequencies whichlie adjacent the resonance frequency and at moderate load, there is riskthat the resonance frequency will be changed to such an extent as toinactivate the drive circuit.

It is also known that the exchange of one tool tip for another willnormally change the impedence value of the tool arrangement, such asresistance value, capacitance value and/or inductance value included inthe first oscillation circuit, to such an extent that the resonanceoscillation frequency will lie in the marginal range of said function orcompletely outside said range, resulting in a functional deficiency. Bythis is meant that the minimum impedence frequency is separate from theseries resonance frequency, which makes it difficult to follow thechanges in the series resonance frequency.

It is difficult, if not impossible, to regulate the frequency of thesupply voltage with the aid of prior known techniques, such that saidfrequency will comply with a resonance frequency applicable to thechanged resonance frequencies of the two parallel-connected oscillationcircuits.

It is known that a drive circuit of the aforesaid kind, functioning todrive a tool arrangement which oscillates at resonance frequency,incorporating a fixed inductance, will permit a frequency change ofabout +/- 2 kHz around the resonance frequency before the requisitecoaction between drive circuit and tool ceases to take place.

None of the earlier known constructions of this kind incorporate meansfor switching between a high-power-state, for operating the tool tip,and a low-power-state, for "stand-by" function or preparatory function.

DISCLOSURE OF THE PRESENT INVENTION Technical Problems

When considering the earlier standpoint of techniques as describedabove, and when considering the technical considerations that haveearlier been the guiding influence for one of normal skill in thistechnical field, it will be seen that in the case of an arrangement fordriving a high-frequency oscillating tool arrangement which includes,inter alia, a device (crystal) whose form changes with changes involtage, and in which there is used an electric drive circuit which isintended to apply to said device or said crystal an alternating voltagewhose frequency is adapted, via a first control circuit, to a valuewhich corresponds momentarily to the resonance frequency of the reactiveelement which varies during operation and during a working process, atechnical problem resides in realising the significance of utilizing asa control parameter for the first control circuit the momentary phasedifference between the prevailing current and voltage values withrespect to said alternating voltage.

A more qualified technical problem will be seen to reside in realizingof the significance of being able to use a further control circuit, asecond control circuit, for maintaining a second resonance circuit inresonance, irrespective of the prevailing alternating voltage frequency.

Still a more complex technical problem is one of realising thesuitability of permitting the second control circuit to control aninductive element incorporated in an oscillation circuit (secondoscillation circuit) having a capacitive element which corresponds tothe tool arrangement concerned, such that the second oscillation circuitwill remain in resonance for the prevailing alternating voltagefrequency, wherewith the first control circuit is able to control thealternating voltage frequency such that the first oscillation circuitwill tend to be in resonance, despite the changes in impedence valuecaused by the operating conditions, and particularly in spite of thechanges in the capacitance and/or inductance values of the capacitiveand/or the inductive element.

When considering the earlier standpoint of techniques, as describedabove, it will also be seen that a technical problem resides in theprovision of a control circuit by means of which an inductance valueincorporated in the second oscillation circuit can be automatically andadaptively adjusted in dependence on frequency, so as to provide anautomatic and adaptive resonance, valid in combination with theresonance frequency valid for the first resonance circuit, havingimpedence values, such as capacitance and/or inductance values whichvary with the operating conditions.

Another technical problem is one of realising that, from an electricalaspect, a high-frequency oscillating tool can be considered as twoparallel-connected oscillation circuits where the magnitudes (impedencevalue, capacitance value, inductance value and resistance value) of theoscillation circuits can be varied by different criteria, and on thebasis of this realisation to realise that the first control circuit canbe constructed for a much larger frequency spectrum when the firstcontrol circuit is able to cause the changes in the resonance frequencyof the first oscillation circuit to produce a corresponding change inthe frequency of the supply voltage, while the second oscillationcircuit is guided and adapted to be in resonance, essentiallyirrespective of the prevailing alternating voltage frequency.

A further technical problem is one of realising the advantages that areafforded when the aforesaid second oscillation circuit includes asimple, adjustable inductance whose value is constantly adapted to theprevailing series resonance frequency and the alternating voltagefrequency.

Another technical problem is one of realising that a change in supplyvoltage frequency to a prevailing resonance frequency value can bereadily achieved when the timewise zero crossings of the current andvoltage curves are permitted to form regulating magnitudes in the firstcontrol circuit.

It will also be seen that in the case of a tool arrangement of theaforedescribed kind, a technical problem resides in realising thoseadvantages that are associated with the provision of a purely vibrationtool mode, and that this mode can be obtained by adjusting the frequencyto phase similarlity with the current and voltage curve, in combinationwith perfect adaptation.

Another technical problem in this regard is one of realising that thenecessary adaptation of the two parallel-connected resonance circuitscan be achieved primarily by controllably changing the frequency towardsresonance in the first resonance circuit through the first controlcircuit, in accordance with the operating conditions, and therewith, andin dependence thereon, change said adjustable inductance value towardsresonance or full adaptation of the second resonance circuit.

Another technical problem is one of enabling the ready use of anadjustable and adaptable inductance included in the second oscillationcircuit, and therewith realise the advantage that when the resonancefrequency in the first resonance circuit is changed automatically bywear in the tool used, the first control circuit will accompany thisslow change in resonance frequency and the resonance frequency changecaused by the actual working conditions or momentary operationconditions, without the control circuit becoming inoperative.

When considering the earlier standpoint of techniques, as describedabove, it will be seen that a further technical problem resides in theprovision of a second control circuit which will enable the inductancevalue to be controllably adapted to changes in the tool resonancefrequency of such large magnitudes that the resonance circuit will be inresonance, even though the tool frequency should decrease or increasefar beyond the earlier known range of +/-2 kHz.

It will also be seen that a technical problem is one of creatingconditions, with the aid of simple means, such that both of theresonance circuits will be in resonance, even when the frequency shiftsare as large as +/-5 kHz, and preferably above +/-10 kHz.

It will also be seen that a technical problem is one of realising thatthis adapted adjustment of the inductance value can be achieved with theaid of a transformer which is saturated to different degrees through ad.c. supply, and therewith exhibits different inductance valuescorresponding to prevailing resonance frequencies.

It will also be seen that a technical problem within this technicalfield is one of realising the significance of using a transformer havinga centre leg and of supplying the direct current to one of the legs andutilizing, in a known manner, the fact that an increasing degree ofsaturation will decrease the inductance in remaining windings, which arepreferably connected in series.

A further technical problem is one of realising the advantages affordedwhen the first electrical control circuit includes first means operativeto determine the phase position of the current and voltage curves in thealternating voltage supplied to the tool arrangement, and to utilizesecond means for generating frequency changes in the alternating currentapplied to the tool, such as to generate a new resonance-creatingfrequency value.

Another technical problem is one of realising the simplifications andimproved adjustment possibilities, from a technical coupling aspect,that can be achieved when utilizing the fact that the current andvoltage curves will be in phase with one another even in a complexresonance circuit which oscillates at resonance frequency, and also bylocking the resonance frequency at a value at which the prevailingcurrent and voltage values are in phase, and adjusting the frequencyvalue up or down, immediately the current and voltage values are-drivenout of phase in a predetermined direction or sense.

It will also be seen that a technical problem is one of realising thatsaid second means shall include two known phase-locking loops and thatthese two phase-locking loops shall be counter-connected so as to enablethe internal, frequency-dependent phase shifts of the loops to beeliminated, thereby enabling an evaluated time difference between thezero crossings or phase difference of the voltage and current values tobe formed, therewith to generate a changed frequency from the one loop.

When considering one or more of the aforementioned technical problems,it will be seen that a technical problem resides in realising thosecircuitry simplifications which can be achieved when the necessaryvariations in energy supplied to the tool are effected by solelyregulating prevailing voltage levels up and down, therewith to maintaina constant particle speed for the tool tip concerned and the prevailingseries resonsance.

When considering the technical contemplations which have succeeded inproviding a solution to one or more of the aforesaid technical problems,a still more complicated technical problem is one of realising that oneor more of the proposed solutions actually form the basis on which a lowenergy consuming "stand-by" facility or preparatory facility can beprovided with the aid of simple means, this facility reducing the energyconsumption of the tool and lowering internal heating of said tool.

A further technical problem resides in providing this "stand-by"facility with the aid of very simple circuit means and with an automaticcut-in and cut-out function.

Still a further technical problem is one of realising that with the aidof simple circuit means, the standby function can be initiated solely byapplying the tool tip to a material or an underlying surface, since thiswill cause a change in resonance which controls the activation of a highenergy level.

It will also be seen that a technical problem is one of realising theadvantages afforded by evaluating a predetermined time period over whichno adjustment has been made and utilizing this circumstance as anindication that the tool arrangement has not been used and therewithcontrol the drive circuit such that the tool is switched to a lowerlevel of energy input.

Another technical problem is one of realising the significance ofgenerating sufficient energy to drive the tool in resonance frequencywhen deactivating, so that the drive circuit will not be deactivatedwhen switching-on.

It will also be seen that a technical problem is one of driving ahigh-frequency oscillating tool arrangement of high efficiency with theability of providing large changes in resonance frequency whilenevertheless creating conditions which will enable the two resonancecircuits to operate within a frequency range for a common resonancefrequency.

It will also be seen that in the case of a circuit arrangement which hassuccessfully solved one or more of the aforesaid technical problems, afurther technical problem resides in the provision of conditions suchthat when starting the high-frequency oscillating tool arrangement, thedrive circuit can be set to a fundamental frequency or resonancefrequency adapted to idling conditions and therewith create conditionswhereby the regulatable inductance value can be adapted so that the setresonance frequency will occur and be valid for the second resonancecircuit.

It will also be seen that a technical problem resides in the provisionof a simple, automatic amplifying circuit which is based on theassumption that the current delivered to the tool shall be constant.

Finally, it will be seen that a technical problem resides in theprovision of an inductance which belongs to a self-adapted drive circuitsuch as to achieve a purely vibrational mode and power adaptation of thetool, by automatically adjusting the inductance value to the prevailingresonance frequency, and also of realising the advantages that areafforded by the use of dual-connected phase-locking loops which, whenthe tool is started-up, will automatically generate the resonancefrequency for the tool working and control point.

SOLUTION

For the purpose of solving one or more of the aforesaid technicalproblems, the present invention provides an arrangement for driving ahigh-frequency oscillating tool arrangement, and then particularly theuse of a tool arrangement of the kind which includes, inter alia, adevice, in the form of a crystal, which changes form when subjected to achange in voltage, and the use of an electric control circuit which isconstructed to generate an alternating voltage which can be applied tosaid device and the frequency of which is adjusted, through a firstcontrol circuit, to a value which corresponds momentarily to theresonance frequency of the reactive element which varies duringoperation and/or a working operation.

In accordance with the present invention, the first electrical controlcircuit is constructed so as to control momentary or instantaneousfrequency in response to the momentary or instantaneous phase differencebetween the prevailing current and voltage values of said alternatingvoltage.

A second control circuit is provided for controlling the momentary orinstantaneous inductance value of an inductive element included in anoscillation circuit with a capacitive element corresponding, inter alia,to the form-changing device and having a (fixed) capacitance value, suchthat a prevailing alternating voltage frequency will impart to theinductive element an inductance value which corresponds to resonance atmomentary frequency.

As preferred embodiments within the scope of the inventive concept, afirst resonance circuit whose inductance and capacitance values vary independence on momentary operating conditions of the tool arrangement isintended to be supplied with an alternating voltage whose frequencyvalue can be varied by means of a momentary resonance frequency valueapplicable to the first resonance circuit, and an adjustable inductanceincluded in a second resonance circuit is adjusted to a frequencydependent value which, together with a capacitance value assigned to thetool, gives resonance at the resonance frequency of the first resonancecircuit.

It is also proposed that the first control circuit will so regulate thefrequency of a Supply voltage that said frequency conforms with theresonance frequency of the momentary inductance and capacitance valuesvalid for the first resonance circuit, whereas adjustment of theadjustable inductance value of the second resonance circuit is effectedautomatically towards the frequency of the supply value.

The current and voltage values applicable for the supply voltage can beevaluated and their respective phase positions with signs aredeterminative for increasing or decreasing the frequency of the supplyvoltage.

If the voltage lies before the current, the frequency is decreased,whereas an increase in frequency takes place when the current liesbefore the voltage.

The phase position or the time distance between the momentary phasevalues of the voltage and current, for instance at zero-crossings,constitutes a frequency change control magnitude.

It is also suggested that said adjustment of the inductance value willresult, through said second control circuit, in resonance frequencies ofthe resonance circuit which lie within a frequency variation rangegreater than 5 kHz around a selected central resonance frequency for thetool arrangement, preferably a frequency variation range greater than 10kHz.

The inductance value is adjusted with the aid of a transformer which issaturated to different degrees through a controllable direct currentsupply, and it is particularly proposed that the transformer isconfigured With a centre leg. The direct current is then supplied to oneof the legs, such that an increase in the degree of saturation willresult in a decrease in the inductance of remaining windings. Thewindings will preferably be connected in series.

It is also proposed that the first electrical control circuit willinclude known first means for determining the phase position of thecurrent and voltage curves of the alternating voltage applied to thetool arrangement, and known second means for generating frequencychanges in the alternating current supplied to the tool arrangement.

A generated frequency is intended to lock on a frequency value at whichthe prevailing current and voltage values lie in phase.

It is also proposed that the first control circuit includes twocounter-connected phase-locking loops which will lock to the current andvoltage curves when said curves are in phase and pass the zero crossingsimultaneously.

Variations in the supply of energy to the tool are effected by solelyadjusting the amplitude of the alternating voltage.

It is also suggested that the voltage and/or current connected to thetool arrangement can be supplied in one of a number of energy modes orstates, such as a high-energy, tool operating state, and a low energystate intended for a "stand-by" tool function.

The requisite switching between one state and another takes placeautomatically, subsequent to fulfilling one or more criteria.

One of these criteria may be switching to a lower level, a so-called"stand-by" or preparatory level subsequent to the lapse of apredetermined time period over which no frequency adjustment has beenmade, thereby to reduce the amount of heat generated in the tool duringthose times periods in which the tool is not in use.

ADVANTAGES

Those advantages primarily associated with an arrangement in accordancewith the invention reside in the creation of conditions which in acomplex oscillation circuit comprising two mutually separate resonancecircuits, the inductance response can be varied so that thehigh-frequency oscillating tool arrangement will constantly be suppliedby an automatically selected series resonance frequency, irrespective oflarge changes in resonance frequency caused by the working tool, thetype of tip used and the material and/or the load to which it issubjected.

A first control circuit is intended to change the frequency of thesupplied alternating voltage towards resonance of a first resonancecircuit which includes, inter alia, inductive and capacitive elementswhose values are changed with working conditions, and a second controlcircuit is intended to change the inductance value of the inductiveelement of a second resonance circuit so that said resonance circuitwill be in resonance irrespective of the frequency of the alternatingvoltage, said second resonance circuit including a capacitive elementwhose value is changed by a crystal used in said arrangement and onlynegligibly by the form, material and size of the tool tip used.

Another advantage resides in the ability to supply energy to the tool ata lower level when no such adjustment has been made over a predeterminedtime period, therewith reducing the generation of heat in the tool overthose periods in which the tool is not used.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of an arrangement intended for driving ahigh-frequency oscillating tool arrangement, intended for working anobject, will now be described in more detail with reference to theaccompanying drawings, in which

FIG. 1 is a block schematic which illustrates the principle constructionof a high-frequency oscillating tool arrangement having connectedthereto an electrical drive circuit, shown in a correspondinglysimplified form, for driving the high-frequency oscillating toolarrangement, said arrangement including a first oscillation circuitcomprising a capacitance and an inductance whose values, inter alia, canbe varied in dependence on the working conditions and the material fromwhich the tool tip is made, and a second oscillation circuit whichincludes a crystal-related capacitance and an inductance which can beinfluenced by a second control circuit;

FIG. 2 is a block schematic which illustrates the tool arrangement ofFIG. 1 in more detail;

FIG. 3 is a more detailed circuit diagram of a second control circuitillustrated in FIG. 2, said second circuit having the form of aself-adjusting adaptation circuit;

FIG. 4 is a more detailed circuit diagram of the first control circuitillustrated in FIG. 2;

FIG. 5 is a more detailed circuit diagram of a "stand-by" blockillustrated in FIG. 2; and

FIG. 6 illustrates a number of process curves and phase curves which areintended to illustrate the inventive regulating function and theregulating function of known control circuits.

DESCRIPTION OF EMBODIMENT AT PRESENT PREFERRED

FIG. 1 is a block schematic illustrating the principle construction of ahigh-frequency oscillating tool arrangement I and an electric drivecircuit 2 connected to said arrangement.

The tool arrangement I of FIG. 1 is illustrated as an equivalent,simplified electrical circuit diagram and includes a first oscillationcircuit C1, L1 and R, where at least the capacitance value of thecapacitance C1 and the inductance value of the inductance L1 varystrongly in dependence on the prevailing tool operating conditions, andparticularly the tip 1b of the tool.

The tool arrangement 1 can also be considered to include a furthercapacitance C2, whose capacitance value does not vary appreciably withprevailing tip operating conditions, but can be considered to have aconstant capacitance value, or at least a substantially constantcapacitance value of the crystal structure.

This capacitance C2 is included in a second oscillation circuit C2, L2,where the inductance value of the inductance L2 can be adjusted in amanner described in more detail here below.

The first oscillation circuit C1, L1 (A) is in resonance throughfrequency adaptation from a first control circuit 7, and the secondoscillation circuit C2, L2 (B) is in resonance through inductance-valueadaptation from a second control circuit 4, for each momentary frequencyapplicable for the alternating voltage supplied.

Thus, the oscillation circuit C2, L2 (B) is in resonance irrespective ofthe momentary alternating voltage frequency applied to the tool or tothe first oscillation circuit C1, L1 (A).

The circuit 6 is intended to detect the momentary current and voltagevalues applicable for the supplied alternating voltage.

The circuit 10 is a regulating circuit which is able to regulate thegenerated frequency via the transformer T1, in response to a signalobtained from the circuit 7.

A circuit 6' is intended to detect prevailing current values and tosend, via a circuit 611, a signal to the circuit 10 which regulatespower with constant current value.

FIG. 2 is a block schematic which illustrates an arrangement for drivinga high-frequency, oscillating tool arrangement 1 and an electric drivecircuit 2 intended for driving the arrangement 1.

The tool arrangement 1 includes a device 1a, in the form of one or more,normally two piezo electric crystals, which changes/change form inresponse to a change in voltage, and there is used an electric drivecircuit 2 which is constructed to apply an alternating voltage to thecrystal 1a through conductors 3, 3'.

The tool arrangement illustrated in FIG. 2 also includes a tool tip 1bwhich can be readily exchanged for other tips, which then normallyproduce another resonance frequency.

Since a tool arrangement 1 which includes one or more crystals 1a and areadily exchangeable tool tip 1b is known to the art, the toolarrangement will not be described in more detail.

The principle construction of the drive circuit 2, according to FIGS. 1and 2, and a preferred embodiment according to FIGS. 3-5 will now bedescribed.

With reference to FIG. 1, there is first shown an equivalent, simplifiedelectrical circuit for the tool arrangement 1. From an electrical pointof view, this circuit can be considered to comprise a resistance R, acapacitance C1 connected in series with an inductance L1, and acapacitance C2 connected in parallel therewith.

The capacitance C1, the inductance L1 and the resistance R form a firstoscillation circuit A.

It can be assumed that the capacitance value C1 and the inductance valueL1 will vary with the load prevailing on the working tip of the tool,whereas its fundamental value is at least dependent on the form, sizeand material of the tool tip. It should be noted that the resonancefrequency selected will also change slightly as the tool tip becomesworn.

It follows from this that the first oscillation circuit A cannot haveconstant values in time, but that these values will vary strongly. Thismeans that the adapted resonance frequency will also vary.

It will be readily understood that changes in resonance frequency willoccur when the tool tip is applied to material or a workpiece to beworked. A change of tool tip will also normally result in a change inresonance frequency.

From an electrical aspect, this means that the capacitance value C1 andthe inductance value L1 will change in time and in dependence onprevailing operating conditions.

The arrangement also includes a second Oscillation circuit B whichincludes a capacitance C2, the value of which can be considered to beconstant or at least substantially constant and will depend on thenature of the crystal 1a used in the arrangement. A more detaileddescription of this is found in "Piezoelectric ceramics" published byMullard Limited, Torrington Place, London WCIE 7HD, England.

In accordance with the inventive principles, an inductance L2 formingpart of an electrical second control circuit in the second oscillationcircuit B can be given different inductance values, which can beadjusted in a manner described in more detail herebelow.

The invention is based on the understanding that the twoparallel-connected resonance circuits will always operate in a commonresonance frequency, irrespective of the resonance frequency changesgenerated in time by the first resonance circuit, for instance when thetool tip works the material.

Thus, it is known that an uncontrolled change of the capacitance valuesand/or inductance values of a resonance circuit will result in acorrespondingly uncontrolled change in resonance frequency, and inaccordance with the present invention., this is considered to apply tothe first resonance circuit A.

It is also known that a change in the inductance and/or capacitancevalue of a resonance circuit as a result of a frequency change can causethe resonance circuit to adapt to resonance, despite the frequencychange, and in accordance with the invention, this shall apply to thesecond resonance circuit B.

FIG. 3 is a principle diagram of a second control circuit 4 in the formof a self-adjusting adaptation circuit 4 which is intended to changeautomatically the inductance value L2 of the second resonance circuit B,so that this resonance circuit will be in resonance at each momentarilyoccurring frequency on the supply line 5, 5' or 3, 31.

The control circuit 4 causes the second resonance circuit B to beconstantly in resonance.

In order to provide a variable inductance value L2, there is used atransformer T2 which has three legs. One of these legs, the centre leg,is provided with a d.c. coil 31 which functions to saturate the core todifferent degrees of saturation and therewith different inductancevalues (L2) for different frequencies, in response to the value of thecurrent.

It may be suitable to change the core area of certain legs so as toobtain an appropriate inductance value and an appropriate inductancevalue variation in response to variation and magnitude of the directcurrent.

The voltage supplied to the tool 1 is connected to earth through thewindings 32, 33 on the two outer legs of the transformer T2.

The two series-connected windings 32 and 33 and a resistance 34 of thetransformer on the one hand, and a capacitor 35 and a resistor 36 on theother hand, form a bridge coupling. As soon as the bridge couplingproduces an output signal on line 37 and line 37' respectively, thissignal is amplified in an amplifying circuit 38 and is supplied,(rectified and amplified), to said centre leg and the direct currentwinding 31.

The voltage values occurring on the conductors 37 and 37' are rectified,whereafter the voltage difference is integrated and utilized to controlsaid current supply or amplifying circuit 38.

Since these circuits are well known, they will not be described indetail.

It should be mentioned, however, that the capacitance value of thecapacitance 35 will preferably be equal to the capacitance value of thecapacitance C2 divided by a constant k.

The resistor 34 has a resistance value which corresponds to theresistance value of the resistor 36, multiplied by said constant k.

The constant k shall be selected so that the bridge coupling will notinfluence adaptation.

A positive output signal between conductor 37 and 37' respectivelyproduces an increase in direct current and a negative output signalproduces a decrease in direct current, wherein the value of theinductance L2 will be determined by the value of the direct current andwill constantly adapt so that the second resonance circuit B is inresonance at a frequency which corresponds to the frequency of thecurrent supplied to the tool.

This resonance frequency applies to a common resonance of the complexresonance circuit which includes an adapted inductance value for theinductance L2 and the capacitance C2 and prevailing values for theinductance L1 and the capacitance C1 which can vary as a result of theoperating conditions.

The self-adjusting circuit 4 is thus supplied with a voltage present onthe conductors 5, 5', this voltage being further supplied to thecrystals 1a of the tool arrangement 1, through conductors 3, 3'.

The voltage value occurring on the conductor 5 is detected through acircuit 6 and delivered to the first control circuit 7.

The current value occurring on the conductor 5' is detected anddelivered to the first control circuit 7, through a circuit and anamplification S. The control circuit 7 is connected to a drive circuit10 which supplies the aforesaid transformer T1 through a conductor.

FIG. 4 is a principle diagram of a first control circuit 7 whichincludes two counter-connected, phase-locking loops. (PLL circuits,Phase Locked Loop circuits) 41 and 42.

Phase locking loops are known to the art, and consequently theoperational function of these loops will not be described in detail,although FIG. 4 illustrates a circuit diagram applicable to twocounterconnected PLL circuits.

It will be seen that the voltage value is applied to the circuit 41,whereas the current value is applied to the circuit 42.

In the absence of a phase difference between the current and voltagevalues 5, 5', the circuit 42 delivers a signal whose frequency isfiltered in a filter 45 and amplified in the drive circuit 10 anddelivered on the conductors 5, 5' as a resonance frequency for the twotuned resonance circuits A and B.

When the tool tip lb is loaded, the resonance frequency of the firstresonance circuit A will change and the current and voltage values onthe conductors 5, 5' will be in phase with one another.

The amplitude of the voltage and current values occurring on theconductors 5, 5' is limited and amplified to square waves in the circuit41 and 42 and the time difference is evaluated with signs for respectivezero crossings. This time difference and sign generates in the circuit42 a frequency change for the outgoing signal, via the filter 45 and thedrive circuit 10.

This change is selected so that the first resonance circuit A will be inthe resonance frequency. The second resonance circuit B automaticallyadjusts to the new resonance frequency, by changing the value on theinductance L2.

The phase-locking loops or circuits 41 and 42 are so coordinated thatthere is delivered from the circuit 42 a signal whose value is dependenton the phase difference, and the internal frequency-dependent phaseshifts of the phase-locking loops are eliminated through the negativefeedback, so that the differences between the voltage and current phasesform control signals which controls the frequency of the circuit 42.

The control circuit 7 (according to FIG. 2) is also connected to afrequency instrument 11 and a means 12, which is adapted for repeatedstarts should phase locking not occur, and which is intended forcoaction with a start block 13. This start block 13 is activated withthe aid of a signal on a conductor 14.

The self-adjusting adaptation 4 is also connected with a "stand-by"block or preparatory block 16, which is activated by occurrent voltagevalues. The "stand-by" block 16 is connected with the automaticamplifying circuit 15 through a conductor 18.

FIG. 5 is a principle diagram of a "stand-by" block or preparatory block16.

It will be seen from FIG. 5 that the regulated voltage by means of whichpower is supplied to the tool arrangement 1 is applied to a circuit 50which is connected to a derivation circuit 51, the output of which isconnected, through a delay circuit 52 set at a delay of five seconds, toan amplifier 53 included in the circuit 15, this amplifier controllingthe supply of current to the tool 1 through the drive unit 10.

It will be evident from this that when the circuits 50 and 51 aresupplied with constant voltage, the derivative will be 0 and the signalwill then throttle the amplifier 53 so that the drive circuit 10 willsupply current which exhibits a value of only 1/10th of the supplycurrent normally required.

In this operational state of the arrangement, the arrangement 1 issupplied with a low level of energy, i.e. is in a low-energy stateduring those periods of time in which the tool is not in use, althoughwith resonance adaptation of the aforedescribed nature.

It is evident that intiation of the "stand-by" block can be effectedwith the aid of other control parameters than the aforesaid voltagevalue.

When the resonance frequency is changed, there is produced on thederivating circuit 51 an output signal which opens the amplifier 53,which changes the amplification in the drive circuit 10 so as to supplyfull power or operational power.

The invention is based on the realisation that when the drive circuit 2drives the tool arrangement at a resonance frequency of, for instance,30 kHz and the tool tip is applied to a workpiece, it can be assumedthat the resonance frequency of the one resonance circuit will increaseto 33 kHz.

This increase in frequency is normally sufficient to deactivate anearlier known adaptation, although in accordance with the presentinvention,.the frequency is now increased and the inductance value ofthe inductance L2 correspondingly adjusted.

Should the work carried out by the tool tip be of such nature as tocause the resonance frequency of one resonance circuit A to fall to alevel of 20 kHz for Instance, the inductance value L2 of the secondresonance circuit B will be adjusted correspondingly so that thisresonance frequency will also lie at 20 kHz.

From a practical aspect, it has been found convenient to adaptadjustment of the inductance value in a manner to give a resonancecircuit within a frequency variation range greater than 10 kHz for thetool, practically not larger than 15 kHz.

FIG. 6A illustrates the process and argument curves as a function of thefrequency of 30 kHz for a perfect, parallel-adapted crystal 1a.

It will be seen from this Figure that the series resonance frequencies,minimum impedence frequencies and real impedence frequencies coincideand that frequency adjustment can be effected by utilizing the positivevalue of the derivative at the intersection point 150 applicable toseries resonance.

FIG. 6B illustrates the process and argument curves as a function of thefrequency of a 30 kHz paralleladapted crystal 1a with its seriesresonance 200 shifted to 32 kHz. The series resonance frequencies,minimum impedence frequencies and real impedence frequencies do notcoincide and, consequently, it is impossible to adjust an earlier knowndrive circuit within limits above say +/-2 kHz.

Finally, FIG. 6C illustrates the process and argument curves as afunction of the frequency of a 30 kHz parallel-adapted crystal 1a withits series resonance 200' shifted to 35 kHz. The series resonancefrequencies, minimum impedence frequencies and real impedencefrequencies do not coincide.

It is seen that in earlier known techniques, no real phase positionaround the series resonance frequency is obtained for frequencies higherthan 32 kHz.

The curves are mirror reversed at frequencies of 28 kHz and 25 kHzrespectively.

FIG. 6A illustrates adaptive adaptation within the recited frequencyrange.

A SUMMARY DESCRIPTION OF THE METHOD OF OPERATION Starting Sequence

When starting the arrangement, the start block 13 is activated andproduces a signal which sets the control circuit 7 to a state in which acentral frequency is generated, 30 kHz, while simultaneously loweringthe amplification through the circuit 15.

In this way, the adaptive adaptation in the circuit 4 will adjust to aresonance frequency of 30 kHz.

In this operational state, the second resonance circuit B is inresonance.

The start block 13 then relinquishes its influence through the controlcircuit 7 and the circuit 15.

Complete parallel-adaptation of the two resonance circuits requiresadaptation of the resonance frequency of the first resonance circuit A,which is effected by adaptive adaptation of the resonance frequency inaccordance with the following.

Adaptive Adaptation

If it is assumed that the first resonance circuit A lies outside theresonance frequency of the second resonance circuit B, automaticadaptation of the frequency is required.

This is effected by detecting the current and voltage values occurringon the conductors 3' and 5.

These are dampened (8, 6) prior to being delivered to respectivecircuits 41, 42 (PLL circuits). The circuits 41, 42 evaluate the phasepositions of the current and the voltage by establishing the time pointsof the zero crossings.

If the voltage lies before the current, the frequency is reduced untilthe phase position "0" occurs.

If the current lies before the voltage, the frequency is increased untilthe phase position "0" occurs.

The inductance L2 changes automatically with each frequency change, sothat the second oscillation circuit will lie in resonance.

The following circumstances should be observed in order to obtain anunderstanding and interpretation of the characteristics of theinvention.

In respect of FIG. 2, a simplification is that, in practice, more thanone resonance frequency is found and that the resonance pattern isperiodic to the extent that the resonance pattern is repeatedperiodically during a tool-tip change, or shortening of the tool tip.

The resonance pattern is disturbed by abrupt changes in area, whereseveral standing wave patterns become more or less pronounced, andconsequently the tool is preferably constructed with requisiteadaptation to this particular circumstance and to the dimensions of thecrystal.

When starting-up, the resonance frequency which lies closest to 30 kHzis chosen, but if the Q-value of the series resonance circuit is toolow, the adaptive adaptation will select a more stable resonancefrequency when load is applied.

It will be understood that the invention is not restricted to theaforedescribed exemplifying embodiment thereof, and that modificationscan be made within the scope of the inventive concept illustrated in thefollowing claims.

We claim:
 1. A system for driving a high-frequency oscillating toolarrangement (1), which includes; inter alia, a device (1a), such as apiezoelectric crystal, whose form will change when subjected to changesin voltage; an electric drive circuit (2), adapted to generate analternating voltage, which can be applied to said device (1a), thefrequency of which is given, through a first control circuit (7), avalue which momentarily corresponds to the resonance frequency of afirst oscillating circuit (C1,L1 and R), representing said device (1a)in an equivalent, simplified electrical circuit diagram, in which thereactive elements (L1,C1) vary during a working operation; a secondoscillating circuit (C2,L2), wherein the capacitive component (C2)thereof is representing said device (1a) in an equivalent, simplifiedelectrical circuit diagram, in which said capacitive component (C2) doesnot vary appreciable with prevailing tool operating conditions (can beconsidered to have a constant capacitance value of the crystalstructure), and the inductive component thereof is, via a second controlcircuit (4), given different inductance (L2) values, wherein said firstoscillating circuit (CI,LL and R) and said second oscillating circuit(C2,L2) consitute two parallel-connected circuits, said first and saidsecond oscillating circuits are operating in a common resonancefrequency mode, characterized in that the inductive component (L2) ofsaid second oscillating circuit (C2,L2) is parallel-connected to itscapacitive component (C2), that a required frequency adjustment of thegenerated alternating voltage towards resonance frequency for the firstoscillating circuit (C1,L1) is effectivated by utilizing the positivevalue of the derivative at an intersection point (150), applicable atsaid resonance of an argument curve as a function of the frequency,where minimum impedance frequencies and real impedance frequenciescoincide, and that the difference (time distance at zero-crossing)between momentary phase values of the voltage and the currentconstitutes required frequency change control magnitude, for changingthe frequency of the generated alternating voltage towards resonance forsaid first oscillating circuit.
 2. A system according to claim 1,characterized in that an adjustment of the inductance value (L2),through said second control circuit (4), is adapted to provide resonancefrequencies within a frequency variation range, which is greater than 5kHz for the tool arrangement.
 3. A system according to claim 1,characterized in that the generated frequency is intended to lock on avalue, at which the prevailing current and voltage values are in phase.4. A system according to claim 1, characterized in that said firstcontrol circuit (7) includes two counter-connected phase-locking loops(41,42), to lock to the current and voltage curves when these are inphase and pass the zero crossing.
 5. A system for driving ahigh-frequency oscillating tool arrangement (1), which includes, interalia, a device (1a), such as a piezoelectric crystal, whose form willchange when subjected to changes in voltage; an electric drive circuit(2), adapted to generate an alternating voltage, which can be applied tosaid device (1a), the frequency of which is given, through a firstcontrol circuit (7), a value which momentarily corresponds to theresonance frequency of a first oscillating circuit (CI,L1, and R),representing said device (1a) in an equivalent, simplified electricalcircuit diagram, in which the reactive elements (L1,C1) vary during aworking operation; a second oscillating circuit (C2,L2), wherein thecapacitive component (C2) thereof is representing said device (1a) in anequivalent, simplified electrical circuit diagram, in which saidcapacitive component (C2) does not vary appreciably with prevailing tooloperation conditions and the inductive component thereof is, via asecond control circuit (4), given different inductance (L2) values,wherein said first oscillating circuit (C1,L1 and R) and said secondoscillating circuit (C2,L2) constitute two parallel-connected circuits,said first and said second oscillating circuits are operating in acommon resonance frequency mode, whereby the voltage and/or the current,connected to the tool arrangement, can be supplied in one of severalpower states or modes, a high power state intended for operating thetool and a low power state intended as a "stand-by" function of thetool, whereby the requisite for switching between one state and theother is effected automatically subsequent to fulfilling one or morecriteria, characterized in that the inductive component (L2) of saidsecond oscillating circuit (C2,L2) is parallel-connected to itscapacitive component (C2), that a required frequency adjustment of thegenerated alternating voltage towards resonance frequency of the firstoscillating circuit (CI,L1) is effectivated by utilizing the positivevalue of the derivative at an intersection point (150), applicable atsaid resonance of an argument curve as a function of the frequency,where minimum impedance frequencies and real impedance frequenciescoincide, that the difference (time distance at zero-crossing) betweenmomentary phase values of the voltage and the current constitutesrequired frequency change control magnitude, for changing the frequencyof the generated alternating voltage towards resonance for said firstoscillating circuit, whereby said power supply is witching betweenoperating mode and "stand-by" mode when a predetermined time period haslapsed, during which no adjustment of the voltage or frequency has beenmade, that said second control circuit (4) is connected to a "stand-by"or preparatory block (16), activated by occurrent voltage values andconnected to an automatic amplifying circuit (15), including aderivation circuit (51) and a delay circuit (52), the former, whensupplied with a constant voltage, causing the derivative value to gotowards "0" and throttling an amplifier (53), causing the drive circuit(10) to generate a signal adapted to "stand-by" mode.